In order to transfer energy from a turbine engine, conventional combustion engine, an electric motor or any power generating apparatus to a machine to power the machine, it is typically necessary to join the power generating apparatus to the machine with some sort of coupling means. These apparatuses typically transmit power through an angularly rotating shaft and this power output is typically referred to as torque. The power coupling means is a critical piece of equipment since its failure will typically result in the de-energization of the machine.
When a power generating apparatus having a high horsepower output (e.g. a 1,000 H.P. electric motor) is coupled to a machine having a high angular velocity shaft (e.g., a centrifugal pump), it is critical that the shafts of the devices are aligned as closely as possible. Misalignment will result in a number of problems including adverse vibration levels, premature bearing failure, structural damage, overheating, excessive noise, and high wear rate and failure rate of the coupling. Although it is theoretically possible to perfectly align the shafts of the power generating apparatus and the machine, there are practical limitations including measurement equipment, equipment location, adverse environmental factors, differential rates of thermal expansion during operation, etc. In addition, the design may require a specified amount of articulation. There are couplings in the prior art which permit slight shaft misalignment for high torque, high speed applications, however, the amount of misalignment is typically about 1/2.degree. or less and these couplings are typically of metal construction and very heavy. The primary limitation of the metal couplings is that the materials of construction do not permit high torque and high angular velocity with large shaft misalignment, up to about 10.degree., across a broad temperature spectrum. Such a power coupling must act as a torque transmitting or driving means, and, it must also act as a flexure to permit elastic deformation to compensate for the misalignment.
The power coupling means is particularly crucial in rotary wing aircraft or helicopters. The power coupling means used in helicopters to transfer torque from the power shaft to the helicopter blades is typically referred to as a rotary hub. The rotary hubs of the prior art were complex, metal mechanisms. The disadvantages of these metal rotary hubs were several including weight, corrosion, fatigue, very high maintenance and cost.
One type of coupling means to supplant metal couplings is composite couplings incorporating layers of composite material. Such couplings include an outer reinforcing circular ring and a resin impregnated fiber strand continuously wrapped from a point tangent to a central bore to the outer surface of the ring and then to a corresponding point transversely spaced from the point tangent to the central bore following a geodesic path. Advantages of such couplings include the high strength load carrying characteristics along the continuous length of the filaments. For example, fiberglass has a tensile strength of about 665,000 psi along its length. The tension strength of such filaments is significantly greater than metal components. Composite couplings are disclosed in U.S. Pat. Nos. 4,629,644 and its related case U.S. Pat. No. 4,666,753, and 4,391,594 and its divisional case U.S. Pat. No. 4,569,667.
The divisional patents '594 and '667 are owned by the assignee of the present case and will be described together. In these patents, a lightweight, flexible coupling is disclosed including a reinforcing ring, a pair of hubs each having a shaft extension for connection to either a drive or driven member and resin impregnated filaments wrapped around a pin on one hub on one side of the reinforcing ring to and across the reinforcing ring and then around a pin on the other hub on the opposite side of the reinforcing ring following a geodesic path. The shaft extension of each hub extends transversely outwardly of the filament portion of the coupling to permit attachment of respective drive or driven members thereto. Such shaft extensions are disadvantageous to the coupling since they add unnecessary weight thereto. The wrapping of the filaments around the pins make production of such couplings very difficult. One method to apply the filaments is by hand wrapping. Further, the straight line or geodesic path of the filaments is substantially altered at the hubs where a filament buildup occurs. This can contribute to early fatigue of the filaments and increased cocking stiffness to the coupling.
In related patents '644 and '753, a lightweight flexible coupling is disclosed including a reinforcing ring, a pair of hub sections with bores therethrough and having attachment holes for drive or driven members therein. Resin impregnated filaments are wrapped tangentially from the bore of one hub on one side of the reinforcing ring to and across the reinforcing ring and then tangentially to the bore of the other hub section on the opposite side of the reinforcing ring. The attachment holes are drilled through the filaments thereby breaking their continuous nature and reducing the tension strength characteristics of the filaments by as much as 30%.
Metal attachment sections for composite couplings are desirous to distribute stresses and avoid the fragility of composite materials. Composite materials that are slightly damaged may be susceptible to failure. One of the requisites of incorporating metal attachments is suitable bonding and anchoring of the filaments to the metal attachment sections. Such bonding has not been shown in the described prior art.